1. Field of the Invention
The invention is directed to an apparatus for delivering aerosol to the airways and/or lungs of a patient, and to a method for operating such an apparatus.
2. Description of the Prior Art
In a great variety of ailments of the airways, a standard form of therapy is to supply pharmacologically active substances or water to the airways in aerosol form. The aerosol is generated in an aerosol generator as known, for example, from German Pat. No. 23 46 730 B2.
A known operating mode for arrangements for delivering aerosol is to activate the aerosol generator during the inspiration phase of the patient. Standard, so-called asthma atomizers operate in this way. The aerosol generation can be triggered by the patient or manually by a therapist, whereby an attempt is made to match the point in time of triggering to the inspiration of the patient. It is difficult to set the proper point in time and the proper dose in this manner. An additional problem is that the size of the aerosol droplets fluctuates greatly since they are often subject to a fast modification immediately after being generated. A designated delivery of aerosol to a defined location in the lungs or airways can thus not be reliably achieved.
Other arrangements operate with continuous aerosol generation during the entire respiratory cycle. During respirator treatment, such aerosol generation can disturb respiration under certain circumstances. Further, it is not possible to undertake the aerosol delivery only during a part of the inspiration, as is often desired, or to supply the aerosol only to a certain portion of the airways or lungs. Moreover, the aerosol forms deposits at undesired regions of the airways and/or lungs and only a small part of the frequently extremely expensive substances reach the desired regions in the respiratory tract.
In other known arrangements, the aerosol generator operates unsynchronized relative to the respiratory cycle and generates the aerosol in a container that is not connected to the airways during aerosol generation. The aerosol stored in the container is inhaled, by the patient after the container has been connected to the airways. Particularly in respiratory therapy, this operating mode is technologically complicated when identical quantities of aerosol are to be continuously inhaled or are to be inhaled with frequent repetition.
German Pat. No. 28 09 255 A1, corresponding to U.S. Pat. No. 4,106,503 discloses a dosing system for the aerosol delivery wherein the administration of aerosol ensues during a predetermined chronological duration of 0.1 through 1.0 seconds. The cooling of a thermistor due to the inhaled gas is used as control signal. The thermistor signal triggers the delivery of pressurized gas to an aerosol generator for the predetermined time. Subsequently, the patient ends the respiratory event with pure atmospheric air.
In another known arrangement (German No. 28 40 762 C3, corresponding to U.S. Pat. Nos. 4,186,737 and 4,279,250) for delivering aerosol to the respirtory tracts, a respirator having separate inspiration and expiration lines is connected to a patient. The aerosol generator discharges directly into stream of respiratory gas at the end of an inspiration phase and is again supplied by the atomizer of the inspiration line at the beginning of the next inspiration phase. The intended goal is that the aerosol is supplied during a brief time span in the first part of the inspiration phase.
In order to better set the suitable point in time for the aerosol delivery, a further known arrangement according to German Pat. No. 29 36 433 A1 provides that the aerosol generator is controlled by a signal linked to the control of the ventilation apparatus. The connection of the aerosol stream into the ventilation gas is controlled pressure-dependent or time-dependent. In accord with the desired distribution of the aerosol in the respiratory tract, the aerosol stream is added to the stream of respiratory gas either dependent on an inspiration pressure that has been reached or delayed relative to the beginning of the inspiration phase. To this end, the aerosol generator is connected to the inspiration line between ventilation apparatus and patient. A separate line is provided for the expiration. Further, the duration of the aerosol generation and thus the dose supplied, as well as the droplet size can be set for use in different regions of the respiratory tract. The productivity of the aerosol generator and its spectrum can be varied independently of the stream of respiratory gas.
The problem of precisely setting a suitable point in time in the respiratory cycle in order to selectively supply the desired region in the respiratory tract with aerosol still exists in all of these known arrangements. For example, the pressure in the airways is not always a reliable parameter for the quantity of respiratory gas already supplied. Resistances in the airways such as mucous or a cough on the part of the patient can lead to considerable increases in pressure. Further, the simple time delay at the beginning of the inspiration phase is not always a measure for the quantity of gas delivered. Morover, apart from the unsynchronized aerosol generation in a container which is not connected to the airways, the aerosol in the other arrangements is always generated immediately before inhalation by the patient. As already stated, the problem thus exists that the droplet size of the aerosol is subject to fast modifications and it is thus difficult to obtain a designated droplet size for treating specific regions of the respiratory tract.